Stacked semiconductor devices and methods of forming same

ABSTRACT

Stacked semiconductor devices and methods of forming the same are provided. Contact pads are formed on a die. A passivation layer is blanket deposited over the contact pads. The passivation layer is subsequently patterned to form first openings, the first openings exposing the contact pads. A buffer layer is blanket deposited over the passivation layer and the contact pads. The buffer layer is subsequently patterned to form second openings, the second opening exposing a first set of the contact pads. First conductive pillars are formed in the second openings. Conductive lines are formed over the buffer layer simultaneously with the first conductive pillars, ends of the conductive lines terminating with the first conductive pillars. An external connector structure is formed over the first conductive pillars and the conductive lines, the first conductive pillars electrically coupling the contact pads to the external connector structure.

BACKGROUND

The semiconductor industry has experienced rapid growth due tocontinuous improvements in the integration density of a variety ofelectronic components (e.g., transistors, diodes, resistors, capacitors,etc.). For the most part, this improvement in integration density hascome from repeated reductions in minimum feature size (e.g., shrinkingthe semiconductor process node towards the sub-20 nm node), which allowsmore components to be integrated into a given area. As the demand forminiaturization, higher speed and greater bandwidth, as well as lowerpower consumption and latency has grown recently, there has grown a needfor smaller and more creative packaging techniques of semiconductordies.

As semiconductor technologies further advance, stacked semiconductordevices, e.g., 3D integrated circuits (3DICs), have emerged as aneffective alternative to further reduce the physical size of asemiconductor device. In a stacked semiconductor device, wafers/dies arestacked on top of one another and are interconnected using throughconnections such as through vias (TVs). Some of the benefits of 3DICs,for example, include exhibiting a smaller footprint, reducing powerconsumption by reducing the lengths of signal interconnects, andimproving yield and fabrication cost if individual dies are testedseparately prior to assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1A-5B are top and cross-sectional views of various processingsteps during fabrication of a semiconductor die in accordance with someembodiments.

FIGS. 6A-10B are top and cross-sectional views of various processingsteps during fabrication of a semiconductor die in accordance with someembodiments.

FIGS. 11A-15B are top and cross-sectional views of various processingsteps during fabrication of a semiconductor die in accordance with someembodiments.

FIG. 16 is a flow diagram illustrating a method of forming asemiconductor die in accordance with some embodiments.

FIGS. 17-21 are cross-sectional views of various processing steps duringfabrication of a stacked semiconductor device in accordance with someembodiments.

FIG. 22 is a flow diagram illustrating a method of forming a stackedsemiconductor device in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Embodiments will be described with respect to embodiments in a specificcontext, namely a stacked device, such as a package-on-package (PoP)device, a chip-on-package (CoP) device, or the like. Variousintermediate stages of forming a stacked device are illustrated. Somevariations of the embodiments are discussed.

FIGS. 1A-5B are top and cross-sectional views of various processingsteps during fabrication of a semiconductor die 100 in accordance withsome embodiments, wherein an “A” figure represents a top view and a “B”figure represents a cross-sectional view along the B-B′ line of therespective “A” figure.

Turning first to FIGS. 1A and 1B, the semiconductor die 100 isillustrated. In the illustrated embodiment, the semiconductor die 100comprises a portion of a processed wafer 101 having contact pads 103formed thereon, and a passivation layer 105 formed over the processedwafer 101 and the contact pads 103. The passivation layer 105 ispatterned to form openings 107 in the passivation layer 105 and exposeportions of the contact pads 103.

In some embodiments, the processed wafer 101 comprises a substrate,various active and passive devices on the substrate, and variousmetallization layers over the substrate, which are not explicitlyillustrated in FIGS. 1A and 1B as their inclusion is not necessary forunderstanding various embodiments described below. The substrate may beformed of silicon, although it may also be formed of other group III,group IV, and/or group V elements, such as silicon, germanium, gallium,arsenic, and combinations thereof. The substrate may also be in the formof silicon-on-insulator (SOI). The SOI substrate may comprise a layer ofa semiconductor material (e.g., silicon, germanium and/or the like)formed over an insulator layer (e.g., buried oxide and/or the like),which is formed on a silicon substrate. In addition, other substratesthat may be used include multi-layered substrates, gradient substrates,hybrid orientation substrates, any combinations thereof and/or the like.

In some embodiments, the variety of active and passive devices mayinclude various n-type metal-oxide semiconductor (NMOS) and/or p-typemetal-oxide semiconductor (PMOS) devices such as transistors,capacitors, resistors, diodes, photo-diodes, fuses and/or the like.

The metallization layers may include an inter-layer dielectric(ILD)/inter-metal dielectric layers (IMDs) formed over the substrate.The ILD/IMDs may be formed, for example, of a low-K dielectric material,such as phosphosilicate glass (PSG), borophosphosilicate glass (BPSG),FSG, SiO_(x)C_(y), Spin-On-Glass, Spin-On-Polymers, silicon carbonmaterial, compounds thereof, composites thereof, combinations thereof,or the like, by any suitable method known in the art, such as spin-oncoating, chemical vapor deposition (CVD), plasma enhanced CVD (PECVD),or the like.

In some embodiments, interconnect structures may be formed in theILD/IMDs using, for example, a damascene process, a dual damasceneprocess, or the like. The ILD/IMDs may be patterned usingphotolithography techniques to form trenches and vias. The interconnectstructures are formed by depositing a suitable conductive material inthe trenches and the vias of the ILD/IMDs using various deposition andplating methods, or the like. In addition, the interconnect structuresmay include one or more barrier/adhesion layers to protect the ILD/IMDsfrom diffusion and metallic poisoning. The one or more barrier/adhesionlayers may comprise titanium, titanium nitride, tantalum, tantalumnitride, or other alternatives. The barrier layer may be formed usingphysical vapor deposition (PVD), atomic layer deposition (ALD),sputtering, or the like. The conductive material of the interconnectstructures may comprise copper, a copper alloy, silver, gold, tungsten,tantalum, aluminum, and the like. In an embodiment, the steps forforming the interconnect structures may include blanket forming the oneor more barrier/adhesion layers, depositing a thin seed layer of aconductive material, and filling the trenches and the vias in theILD/IMDs with the conductive material, for example, by plating. Achemical-mechanical polishing (CMP) is then performed to remove excessportions of the interconnect structures. In some embodiments, theinterconnect structures may provide electrical connections between thevarious passive and active devices formed on the substrate.

In some embodiments, the processed wafer 101 may be a logic wafer, amemory wafer, a sensor wafer, an analog wafer, or the like. Theprocessed wafer 101 may be formed using a complementarymetal-oxide-semiconductor (CMOS) process, a micro-electro-mechanicalsystems (MEMS) process, a nano-electro-mechanical systems (NEMS)process, the like, or a combination thereof. As described below ingreater detail, the processed wafer 101 will be singulated to formindividual dies (such as the semiconductor die 100), which will besubsequently packaged to form a stacked semiconductor device.

Referring further to FIGS. 1A and 1B, the contact pads 103 are formed onthe processed wafer 101 over the metallization layers. The contact pads103 electrically couple the processed wafer 101 to external circuitry asdescribed below in greater detail. The contact pads 103 may comprise aconductive material such as copper, tungsten, aluminum, silver, gold,the like, or a combination thereof, and may be formed by anelectro-chemical plating process, an electroless plating process, ALD,PVD, the like, or a combination thereof. In some embodiments, thecontact pads 103 may further comprise a thin seed layer (not shown),wherein the conductive material of the contact pads 103 is depositedover the thin seed layer. The seed layer may comprise copper, titanium,nickel, gold, manganese, the like, or a combination thereof, and may beformed by ALD, PVD, sputtering, the like, or a combination thereof.

In the illustrated embodiment, the conductive material of the contactpads 103, such as aluminum, is deposited over the processed wafer 101and patterned to form the contact pads 103 as illustrated in FIGS. 1Aand 1B. The contact pads 103 may be patterned using photolithographytechniques. Generally, photolithography techniques involve depositing aphotoresist material, which is subsequently irradiated (exposed) anddeveloped to remove a portion of the photoresist material. The remainingphotoresist material protects the underlying material, such as theconductive material of the contact pads 103, from subsequent processingsteps, such as etching. A suitable etching process, such as a reactiveion etch (RIE) or other dry etch, an isotropic or anisotropic wet etch,or any other suitable etching or patterning process may be applied tothe conductive material of the contact pads 103 to remove the exposedportion of the conductive material and form the contact pads 103. Insome embodiments, exposed portions of the conductive material such asaluminum may be etched using a mixture of 80% phosphoric acid, 5% nitricacid, 5% acetic acid, and 10% de-ionized (DI) water. In someembodiments, the contact pads 103 have a width W₁ between about 37 μmand about 110 μm, such as about 54 μm.

In some embodiments, the passivation layer 105 is formed over theprocessed wafer 101 and the contact pads 103. In some embodiments, thepassivation layer 105 may comprise dielectric materials such as siliconnitride, silicon carbide, silicon oxide, silicon oxynitride, low-kdielectrics such as carbon doped oxides, extremely low-k dielectricssuch as porous carbon doped silicon dioxide, the like, or a combinationthereof, and may be formed using CVD, PVD, ALD, the like, or acombination thereof.

Referring to further to FIGS. 1A and 1B, the openings 107 are formed inthe passivation layer 105 to expose portions of the contact pads 103. Insome embodiments, the passivation layer 105 may be patterned usingsuitable photolithography and etching methods. In some embodiments, aphotoresist material (not shown) is formed over the passivation layer105. The photoresist material is subsequently irradiated (exposed) anddeveloped to remove a portion of the photoresist material. Subsequently,exposed portions of the passivation layer 105 are removed using, forexample, a suitable etching process to form the openings 107. In someembodiments, the passivation layer 105 formed of silicon oxide is etchedusing, for example, buffered hydrofluoric acid (HF). In otherembodiments, the passivation layer 105 formed of silicon nitride isetched using, for example, hot phosphoric acid (H₃PO₄). In theillustrated embodiment, top-view shapes of the openings 107 are circles.However, in other embodiments, the top-view shapes of the openings 107may be polygons such as triangles, rectangles, hexagons, or the like. Insome embodiments, the openings 107 have a width W₂ between about 33 μmand about 106 μm, such as about 50 μm. In some embodiments, the width W₁of the contact pads 103 is larger than the width W₂ of the openings 107.

Referring to FIGS. 2A and 2B, a buffer layer 201 is formed over thepassivation layer 105 and the contact pads 103. In some embodiments, thebuffer layer 201 may comprise dielectric materials such asphoto-patternable polymers including, but not limited to, polyimide(PI), benzocyclobutene (BCB), polybenzoxazole (PBO), the like, or acombination thereof. In some embodiments, the buffer layer 201 may beformed using, for example, CVD, a spin-on coating method, or the like.In some embodiments, the buffer layer 201 has a thickness T₁ betweenabout 3 μm and about 10 μm.

In some embodiments, the buffer layer 201 is patterned to form openings203 and expose the contact pads 103. In some embodiments, the openings203 may be formed using suitable photolithography techniques to exposethe buffer layer 201 to light. The buffer layer 201 is developed and/orcured after the exposure. As described below in greater detail, arouting layer is formed in the openings 203 and over the buffer layer201. In some embodiments, the routing layer comprises first conductivepillars and second conductive pillars (such as first conductive pillars401 and second conductive pillars 403 illustrated in FIGS. 4A and 4B)formed in the openings 203 and conductive lines (such as conductivelines 405 illustrated in FIGS. 4A and 4B) formed over the buffer layer201 and interconnecting pairs of the second conductive pillars. In theillustrated embodiment, top-view shapes of the openings 203 are circles.However, in other embodiments, the top-view shapes of the openings 203may be polygons such as triangles, rectangles, hexagons, or the like. Insome embodiments, the openings 203 have a width W₃ between about 13 μmand about 86 μm, such as about 30 μm. In some embodiments, the width W₂of the openings 107 is larger than the width W₃ of the openings 203.

Referring to FIGS. 3A and 3B, a seed layer 301 is blanket deposited overthe buffer layer 201 and the openings 203. The seed layer 301 maycomprise one or more layers of copper, titanium, nickel, gold,manganese, the like, or a combination thereof, and may be formed by ALD,PVD, sputtering, the like, or a combination thereof. In someembodiments, the seed layer 301 comprises a layer of copper formed overa layer of titanium.

Referring further to FIGS. 3A and 3B, a patterned mask 303 is formedover the seed layer 301. In some embodiments, the patterned mask 303comprises a photoresist material, or any photo-patternable material. Insome embodiments, a material of the patterned mask 303 is deposited,irradiated (exposed) and developed to remove portions of the materialand form openings 305, 307 and 309, thereby forming the patterned mask303. In the illustrated embodiment, the openings 305 and 307 exposeportions of the seed layer 301 formed over the contact pads 103 in theopenings 203, and the openings 309 expose portions of the seed layer 301formed over the buffer layer 201. As discussed in greater detail below,first conductive pillars (such as first conductive pillars 401illustrated in FIGS. 4A and 4B) and second conductive pillars (such assecond conductive pillars 403 illustrated in FIGS. 4A and 4B) will beformed in the openings 305 and 307, respectively, to provide electricalconnections to the contact pads 103. Furthermore, conductive lines (suchas conductive lines 405 illustrated in FIGS. 4A and 4B) will be formedin the openings 309 to electrically interconnect pairs of the secondcontact pillars. In the illustrated embodiment, top-view shapes of theopenings 305 and 307 are circles. However, in other embodiments, thetop-view shapes of the openings 305 and 307 may be polygons such astriangles, rectangles, hexagons, or the like. In some embodiments, theopenings 305 and 307 have a width W₄ between about 33 μm and about 106μm, such as about 50 μm, and the openings 309 have a width W₅ betweenabout 15 μm and about 60 μm, such as about 15 μm.

Referring to FIGS. 4A and 4B, first conductive pillars 401 are formed incombined openings formed of the openings 305 and 203 (see FIGS. 3A and3B), second conductive pillars 403 are formed in combined openingsformed of the openings 307 and 203 (see FIGS. 3A and 3B) and conductivelines 405 are formed in the openings 309 (see FIGS. 3A and 3B). In someembodiments, the openings 203, 305, 307 and 309 are filled with aconductive material such as copper, tungsten, aluminum, silver, gold,the like, or a combination thereof, using an electro-chemical platingprocess, an electroless plating process, ALD, PVD, the like, or acombination thereof. Accordingly, the first conductive pillars 401 andthe second conductive pillars 403 have the width W₄ of the openings 305and 307, and the conductive lines 405 have the width W₅ of the openings309. In the illustrated embodiments, the first conductive pillars 401are not directly coupled to other conductive pillars or the conductivelines 405 and pairs of the second conductive pillars 403 are directlycoupled by conductive lines 405. In some embodiments, the conductiveline 405 is separated from two neighboring conductive pillars, such asthe first conductive pillar 401 and the second conductive pillar 403, bya first distance D₁ and a second distance D₂, respectively, asillustrated in FIGS. 4A and 4B. In the illustrated embodiment, thesecond distance D₂ is larger than the first distance D₁. In otherembodiments, the second distance D₂ may be less than or equal to thefirst distance D₁. In some embodiments, the first distance D₁ is betweenabout 15 μm and about 50 μm, and the second distance D₂ is between about15 μm and about 50 μm.

Referring further to FIGS. 4A and 4B, after forming the first conductivepillars 401, the second conductive pillars 403 and the conductive lines405, the patterned mask 303 is removed. In some embodiments, thepatterned mask 303 comprising a photoresist material is removed using,for example, an ashing process followed by a wet clean process.Subsequently, exposed portions of the seed layer 301 are removed using,for example, a suitable etching process. In an embodiment wherein theseed layer 301 comprises a copper layer formed over a titanium layer,the seed layer 301 may be etched using, for example, a mixture of FeCl₃,HCl, and H₂O (for etching copper) and a mixture of H₂O₂, HF, and H₂O(for etching titanium).

Referring to FIGS. 5A and 5B, a protective layer 501 is formed over andsurrounding the first conductive pillars 401, the second conductivepillars 403 and the conductive lines 405. In some embodiments, theprotective layer 501 may comprise dielectric materials such as polyimide(PI), benzocyclobutene (BCB), polybenzoxazole (PBO), the like, or acombination thereof, and may be formed using a spin-on coating method,or the like. During the following description, the passivation layer105, the buffer layer 201, the protective layer 501, the seed layer 301,the first conductive pillars 401, the second conductive pillars 403 andthe conductive lines 405 may be collectively referred to as a routingstructure 503. In some embodiments, the processed wafer 101 may besingulated into individual semiconductor dies (such as the semiconductordie 100) by sawing, a laser ablation method, or the like. Subsequently,each of the dies may be tested to identify known good dies (KGDs) forfurther processing.

As described above, the buffer layer 201 is interposed between thepassivation layer 105 and the first conductive pillars 401, the secondconductive pillars 403 and the conductive lines 405. The use of bufferlayer 201 may advantageously allow reducing or eliminating formation ofcracks in the passivation layer 105 and layers below, which may becaused, for example, by mismatch of coefficients of thermal expansion(CTE) between the passivation layer 105 and the first conductive pillars401, the second conductive pillars 403 and the conductive lines 405.

Referring further to FIGS. 5A and 5B, in some embodiments, the contactpads 103 that are contacting the second conductive pillars 403 may beelectrically decoupled from the various active and passive devices ofthe semiconductor die 100 and may be also referred to as floatingcontact pads. Accordingly, in such embodiments, the second conductivepillars 403 and the conductive lines 405 are not directly coupled to thevarious active and passive devices of the semiconductor die 100. Asdescribed below in greater detail, in some embodiments, one or moreredistribution layers (RDLs) may be formed over the routing structure503 after dicing the processed wafer 101 into individual semiconductordies (such as the semiconductor die 100). In some embodiments, the RDLsmay electrically couple the second conductive pillars 403, thecorresponding contact pads 103 and the conductive lines 405 to thevarious active and passive devices of the semiconductor die 100, forexample, by interconnecting the contact pads 103 that are coupled to thevarious active and passive devices of the semiconductor die 100 to thesecond conductive pillars 403. In other embodiments, the RDLs may notcouple the second conductive pillars 403, the corresponding contact pads103 and the conductive lines 405 to the various active and passivedevices of the semiconductor die 100. In such embodiments, the secondconductive pillars 403 and the conductive lines 405 may act asredistribution lines for one or more external devices coupled to thesemiconductor die 100. For example, a signal from a first externaldevice may travel through the RDLs to a first pillar of a pair of thesecond conductive pillars 403, then through a corresponding conductiveline 405 to a second pillar of the pair of the second conductive pillars403, then again thorough RDLs to reach a second external device oranother RDL of the first external device, bypassing in the process thevarious active and passive devices of the semiconductor die 100. Byforming the routing structure 503 on the semiconductor die 100 beforeforming one or more RDLs, it is possible to advantageously simplify astructure of the RDLs. In some embodiments, the number of one or moreRDLs may be reduced, which in turn may reduce parasitic contributionsfrom eliminated layers of the one or more RDLs.

FIGS. 6A-10B are top and cross-sectional views of various processingsteps during fabrication of a semiconductor die 600 in accordance withsome embodiments, wherein an “A” figure represents a top view and a “B”figure represents a cross-sectional view along the B-B′ line of therespective “A” figure. As described above with reference to FIGS. 1A-5B,the buffer layer 201 completely covers the passivation layer 105. Inembodiments described below, a buffer layer 701 partially covers apassivation layer 605 (see, for example, FIGS. 7A and 7B).

Turning first to FIGS. 6A and 6B, the semiconductor die 600 isillustrated. In the illustrated embodiment, the semiconductor die 600comprises a portion of a processed wafer 601 having contact pads 603formed thereon, and a passivation layer 605 formed over the processedwafer 601 and the contact pads 603. The passivation layer 605 ispatterned to form openings 607 in the passivation layer 605 and exposeportions of the contact pads 603. In some embodiments, the processedwafer 601, the contact pads 603 and the passivation layer 605 may beformed using similar materials and methods as the processed wafer 101,the contact pads 103 and passivation layer 105, respectively, discussedabove with reference to FIGS. 1A and 1B and the description is notrepeated herein. In some embodiments, the openings 607 in thepassivation layer 605 may be formed using similar methods as theopenings 107 in the passivation layer 105 discussed above with referenceto FIGS. 1A and 1B and the description is not repeated herein. In someembodiments, the contact pads 603 have the width W₁ between about 37 μmand about 110 μm, such as about 54 μm. In some embodiments, the openings607 have the width W₂ between about 33 μm and about 106 μm, such asabout 50 μm. In some embodiments, the width W₁ of the contact pads 603is larger than the width W₂ of the openings 607.

Referring to FIGS. 7A and 7B, a buffer layer 701 is formed over thepassivation layer 605 and the contact pads 603. In some embodiments, thebuffer layer 701 may be formed and patterned using similar materials andmethods as the buffer layer 201 (see, for example, FIGS. 2A and 2B) andthe description is not repeated herein. In some embodiments, a thicknessof the buffer layer 701 is equal to the thickness T₁ between about 3 μmand about 10 μm.

In some embodiments, the buffer layer 701 is patterned to form openings703 and expose the contact pads 603. Furthermore, the patterning processof the buffer layer 701 exposes portions of the passivation layer 605,such that a desired pattern of the buffer layer 701 is formed over thepassivation layer 605 and the contact pads 603. In the illustratedembodiment, top-view shapes of the openings 703 are circles. However, inother embodiments, the top-view shapes of the openings 703 may bepolygons such as triangles, rectangles, hexagons, or the like. In someembodiments, the openings 703 have the width W₃ between about 13 μm andabout 86 μm, such as about 30 μm. In some embodiments, the width W₂ ofthe openings 607 is larger than the width W₃ of the openings 703.

A described below in greater detail, a routing layer is formed in theopenings 703 and over the buffer layer 701. In some embodiments, therouting layer comprises first conductive pillars and the secondconductive pillars (such as first conductive pillars 901 and secondconductive pillars 903 illustrated in FIGS. 9A and 9B) formed in theopenings 703 and conductive lines (such as conductive lines 905illustrated in FIGS. 9A and 9B) formed over the buffer layer 701 andinterconnecting pairs of the second conductive pillars. In theillustrated embodiment, a pattern of the buffer layer 701 as viewed fromthe top comprises ring-shaped structures 705 enclosing the openings 703,and rectangular structures 707 interconnecting some pairs of thering-shaped structures 705. In some embodiments, as viewed from the top,the first contact pillars and the second contact pillars may havecircular shapes similar to the ring-shaped structures 705 and theconductive lines may have rectangular shapes similar to the rectangularstructures 707 (see, for example, FIG. 9A).

Referring to FIGS. 8A and 8B, a seed layer 801 is blanket deposited overthe buffer layer 701, the passivation layer 605 and in the openings 703.In some embodiments, the seed layer 801 may be formed using similarmaterials and methods as the seed layer 301 (see, for example, FIGS. 3Aand 3B) and the description is not repeated herein.

Referring further to FIGS. 8A and 8B, a patterned mask 803 is formedover the seed layer 801. In some embodiments, the patterned mask 803 maybe formed using similar materials and methods as the patterned mask 303(see, for example, FIGS. 3A and 3B) and the description is not repeatedherein. In some embodiments, the patterned mask 803 has openings 805,807 and 809 formed therein. In the illustrated embodiment, the openings805 and 807 expose portions of the seed layer 801 formed over thecontact pads 603 in the openings 703, and the openings 809 exposeportions of the seed layer 801 formed over the buffer layer 701. Asdiscussed in greater detail below, first conductive pillars (such as thefirst conductive pillars 901 illustrated in FIGS. 9A and 9B) and secondconductive pillars (such as the second conductive pillars 903illustrated in FIGS. 9A and 9B) will be formed in the openings 805 and807, respectively, to provide electrical connections to the contact pads603. Furthermore, conductive lines (such as the conductive lines 905illustrated in FIGS. 9A and 9B) will be formed in the openings 809 toelectrically interconnect pairs of the second contact pillars. In theillustrated embodiment, top-view shapes of the openings 805 and 807 arecircles. However, in other embodiments, the top-view shapes of theopenings 805 and 807 may be polygons such as triangles, rectangles,hexagons, or the like. In some embodiments, the openings 805 and 807have a width W₄ between about 33 μm and about 106 μm, such as about 50μm, and the openings 809 have a width W₅ between about 15 μm and about60 μm, such as about 15 μm.

Referring to FIGS. 9A and 9B, the first conductive pillars 901 areformed in combined openings formed by the openings 805 and 703, thesecond conductive pillars 903 are formed in combined openings formed bythe openings 807 and 703, and the conductive lines 905 are formed in theopenings 809 (see FIGS. 8A and 8B). In some embodiments, the firstconductive pillars 901, the second conductive pillars 903 and theconductive lines 905 may be formed using similar materials and methodsas the first conductive pillars 401, the second conductive pillars 403and the conductive lines 405 (see, for example, FIGS. 4A and 4B) and thedescription is not repeated herein. Accordingly, the first conductivepillars 901 and the second conductive pillars 903 have the width W₄ ofthe openings 805 and 807, and the conductive lines 905 have the width W₅of the openings 809. In some embodiments, the conductive line 905 isseparated from two neighboring conductive pillars, such as the firstconductive pillar 901 and the second conductive pillar 903, by the firstdistance D₁ and the second distance D₂, respectively, as illustrated inFIGS. 9A and 9B. In the illustrated embodiment, the second distance D₂is larger than the first distance D₁. In other embodiments, the seconddistance D₂ may be less than or equal to the first distance D₁. In someembodiments, the first distance D₁ is between about 15 μm and about 50μm, and the second distance D₂ is between about 15 μm and about 50 μm.

Referring further to FIGS. 9A and 9B, after forming the first conductivepillars 901, the second conductive pillars 903 and the conductive lines905, the patterned mask 803 is removed. In some embodiments, thepatterned mask 803 comprising a photoresist material is removed using,for example, an ashing process followed by a wet clean process.Subsequently, exposed portions of the seed layer 801 are removed usingsimilar methods as the seed layer 301 (see, for example, FIGS. 4A and4B) and the description is not repeated herein.

FIG. 9A illustrates that a top-view pattern of the routing layer,comprising the first conductive pillars 901, the second conductivepillars 903 and the conductive lines 905, is similar to a top-viewpattern of the buffer layer 701, with elements of the top-view patternof the buffer layer 701 having larger sizes than similar elements of thetop-view pattern of the routing layer. In some embodiments, the bufferlayer 701 and the patterned mask 803 may be patterned using masks havingfeatures of same sizes. However, due to process variations, a samefeature of a mask after being transferred to the buffer layer 701 andthe patterned mask 803 may have different sizes depending on materialproperties of the buffer layer 701 and the patterned mask 803, andpatterning methods used. In the illustrated embodiment, an outerdiameter of the ring-shaped structures 705 is larger than the width W₄of the first conductive pillars 901 and the second conductive pillars903, and a width of the rectangular structures 707 is larger than thewidth W₅ of the conductive lines 905. In some embodiments, sidewalls ofthe first conductive pillars 901 and the second conductive pillars 903are separated from corresponding outer sidewalls of the ring-shapedstructures 705 by a third distance D₃ between about 3 μm and about 7 μm,such as about 5 μm, and sidewalls of the conductive lines 905 areseparated from corresponding sidewalls of the rectangular structures 707by the third distance D₃. However, in other embodiments, the thirddistance D₃ may vary depending on properties of patterned materials andpatterning methods used. Accordingly, the outer diameter of thering-shaped structures 705 is equal to W₄+2D₃, and the width of therectangular structures 707 is equal to W₅+2D₃.

Referring further to FIGS. 9A and 9B, due to process variations, some ofthe features that are resolved in the patterned mask 803 may not beresolved in the buffer layer 701. In some embodiments, if features to bepatterned in the buffer layer 701 are less than a critical dimension,such features will not be resolved by the patterning process. In someembodiments, the critical dimension is about 10 μm for the buffer layer701, and the critical dimension is about 8 μm for the patterned mask803. However, in other embodiments, the critical dimensions may varydepending on properties of patterned materials and patterning methodsused. In the illustrated embodiment, the first distance D₁ is less thanthe critical dimension for the buffer layer 701 and the second distanceD₂ is greater than the critical dimension for the buffer layer 701.Accordingly, ring-shaped structure 705 and the rectangular structure 707corresponding to the first conductive pillar 901 and the conductive line905 that are separated by the first distance D₁ are not resolved andform a single continuous structure. Furthermore, ring-shaped structure705 and the rectangular structure 707 corresponding to the secondconductive pillar 903 and the conductive line 905 that are separated bythe second distance D₂ are resolved and form two disconnectedstructures. Moreover, since the critical dimension for the patternedmask 803 is less than the critical dimension for the buffer layer 701,the openings 805, 807, 809 and the corresponding first conductivepillars 901, second conductive pillars 903 and conductive lines 905 arefully resolved as illustrated in FIGS. 9A and 8B.

Referring to FIGS. 10A and 10B, a protective layer 1001 is formed overand surrounding the first conductive pillars 901, the second conductivepillars 903 and the conductive lines 905. In some embodiments, theprotective layer 1001 may be formed using similar materials and methodsas the protective layer 501 (see, for example, FIGS. 5A and 5B) and thedescription is not repeated herein. During the following description,the passivation layer 605, the buffer layer 701, the protective layer1001, the seed layer 801, the first conductive pillars 901, the secondconductive pillars 903 and the conductive lines 905 may be collectivelyreferred to as a routing structure 1003. In some embodiments, theprocessed wafer 601 may be singulated into individual semiconductor dies(such as the semiconductor die 600) by sawing, a laser ablation method,or the like. Subsequently, each of the dies may be tested to identifyknown good dies (KGDs) for further processing.

As described above, the buffer layer 701 is interposed between thepassivation layer 605 and the first conductive pillars 901, the secondconductive pillars 903 and the conductive lines 905. The use of bufferlayer 701 may advantageously allow reducing or eliminating formation ofcracks in the passivation layer 605 and layers below, which may becaused, for example, by mismatch of coefficients of thermal expansion(CTE) between the passivation layer 605 and the first conductive pillars901, the second conductive pillars 903 and the conductive lines 905.

Referring further to FIGS. 10A and 10B, in some embodiments, the contactpads 603 that are contacting the second conductive pillars 903 may beelectrically decoupled from the various active and passive devices ofthe semiconductor die 600 and may be also referred to as floatingcontact pads. Accordingly, in such embodiments, the second conductivepillars 903 and the conductive lines 905 are not directly coupled to thevarious active and passive devices of the semiconductor die 600. Asdescribed below in greater detail, in some embodiments, one or moreredistribution layers (RDLs) may be formed over the routing structure1003 after dicing the processed wafer 601 into individual semiconductordies (such as the semiconductor die 600). In some embodiments, the RDLsmay electrically couple the second conductive pillars 903, thecorresponding contact pads 603 and the conductive lines 905 to thevarious active and passive devices of the semiconductor die 600, forexample, by interconnecting the contact pads 603 that are coupled to thevarious active and passive devices of the semiconductor die 600 to thesecond conductive pillars 903. In other embodiments, the RDLs may notcouple the second conductive pillars 903, the corresponding contact pads603 and the conductive lines 905 to the various active and passivedevices of the semiconductor die 600. In such embodiments, the secondconductive pillars 903 and the conductive lines 905 may act asredistribution lines for one or more external devices coupled to thesemiconductor die 600. For example, a signal from a first externaldevice may travel through the RDLs to a first pillar of a pair of thesecond conductive pillars 903, then through a corresponding conductiveline 905 to a second pillar of the pair of the second conductive pillars903, then again thorough RDLs to reach a second external device oranother RDL of the first external device, bypassing in the process thevarious active and passive devices of the semiconductor die 600. Byforming the routing structure 1003 on the semiconductor die 600 beforeforming one or more RDLs, it is possible to advantageously simplify astructure of the RDLs. In some embodiments, the number of one or moreRDLs may be reduced, which in turn may reduce parasitic contributionsfrom eliminated layers of the one or more RDLs.

FIGS. 11A-15B are top and cross-sectional views of various processingsteps during fabrication of a semiconductor die 1100 in accordance withsome embodiments, wherein an “A” figure represents a top view and a “B”figure represents a cross-sectional view along the B-B′ line of therespective “A” figure. In the embodiment described below, a pattern of abuffer layer 1201 (see, for example, FIGS. 12A and 12B) is differentfrom a pattern of the buffer layer 701 (see, for example, FIGS. 7A and7B). In particular, the pattern of the buffer layer 1201 may be obtainedfrom the pattern of the buffer layer 701 by removing the ring-shapedstructures 705 corresponding to the first conductive pillars 901 fromthe pattern of the buffer layer 701. Since cracks tend to formpredominantly below the conductive lines 905, by removing thering-shaped structures 705 corresponding to the first conductive pillars901 from the buffer layer 701, desired characteristics of thesemiconductor die 1100 are not adversely affected.

Turning first to FIGS. 11A and 11B, the semiconductor die 1100 isillustrated. In the illustrated embodiment, the semiconductor die 1100comprises a portion of a processed wafer 1101 having contact pads 1103formed thereon, and a passivation layer 1105 formed over the processedwafer 1101 and the contact pads 1103. The passivation layer 1105 ispatterned to form openings 1107 in the passivation layer 1105 and exposeportions of the contact pads 1103. In some embodiments, the processedwafer 1101, the contact pads 1103 and the passivation layer 1105 may beformed using similar materials and methods as the processed wafer 101,the contact pads 103 and passivation layer 105, respectively, discussedabove with reference to FIGS. 1A and 1B and the description is notrepeated herein. In some embodiments, the openings 1107 in thepassivation layer 1105 may be formed using similar methods as theopenings 107 in the passivation layer 105 discussed above with referenceto FIGS. 1A and 1B and the description is not repeated herein. In someembodiments, the contact pads 1103 have the width W₁ between about 37 μmand about 110 μm, such as about 54 μm. In some embodiments, the openings1107 have the width W₂ between about 33 μm and about 106 μm, such asabout 50 μm. In some embodiments, the width W₁ of the contact pads 1103is larger than the width W₂ of the openings 1107.

Referring to FIGS. 12A and 12B, a buffer layer 1201 is formed over thepassivation layer 1105 and the contact pads 1103. In some embodiments,the buffer layer 1201 may be formed and patterned using similarmaterials and methods as the buffer layer 201 (see, for example, FIGS.2A and 2B) and the description is not repeated herein. In someembodiments, a thickness of the buffer layer 1201 is equal to thethickness T₁ between about 3 μm and about 10 μm.

In some embodiments, the buffer layer 1201 is patterned form a desiredpattern. In the illustrated embodiments, the buffer layer 1201 ispatterned to form openings 1203, which partially expose some of theopenings 1107 and the contact pads 1103. In some embodiments, thepatterning process of the buffer layer 1201 fully exposes some of theopenings 1107. In the illustrated embodiment, top-view shapes of theopenings 1203 are circles. However, in other embodiments, the top-viewshapes of the openings 1203 may be polygons such as triangles,rectangles, hexagons, or the like. In some embodiments, the openings1203 have the width W₃ between about 13 μm and about 86 μm, such asabout 30 μm. In some embodiments, the width W₂ of the openings 1107 islarger than the width W₃ of the openings 1203.

A described below in greater detail, a routing layer is formed in theopenings 1107 and 1203 and over the buffer layer 1201. In someembodiments, the routing layer comprises first conductive pillars (suchas first conductive pillars 1401 illustrated in FIGS. 14A and 14B)formed in the openings 1107, second conductive pillars (such as secondconductive pillars 1403 illustrated in FIGS. 14A and 14B) formed in theopenings 1203 and conductive lines (such as conductive lines 1405illustrated in FIGS. 14A and 14B) formed over the buffer layer 1201 andinterconnecting pairs of the second conductive pillars. In theillustrated embodiment, a pattern of the buffer layer 1201 as viewedfrom the top comprises ring-shaped structures 1205 enclosing theopenings 1203, and rectangular structures 1207 interconnecting pairs ofthe ring-shaped structures 1205. In some embodiments, as viewed from thetop, the first contact pillars and the second contact pillars may havecircular shapes similar to the ring-shaped structures 1205 and theconductive lines may have rectangular shapes similar to the rectangularstructures 1207 (see, for example, FIG. 14A).

Referring to FIGS. 13A and 13B, a seed layer 1301 is blanket depositedover the buffer layer 1201, the passivation layer 1105 and the openings1107 and 1203. In some embodiments, the seed layer 1301 may be formedusing similar materials and methods as the seed layer 301 (see, forexample, FIGS. 3A and 3B) and the description is not repeated herein.

Referring further to FIGS. 13A and 13B, a patterned mask 1303 is formedover the seed layer 1301. In some embodiments, the patterned mask 1303may be formed using similar materials and methods as the patterned mask303 (see, for example, FIGS. 3A and 3B) and the description is notrepeated herein. In some embodiments, the patterned mask 1303 hasopenings 1305, 1307 and 1309 formed therein. In the illustratedembodiment, the openings 1305 and 1307 expose portions of the seed layer1301 formed over the contact pads 1103 in the openings 1107 and 1203,respectively, and the openings 1309 expose portions of the seed layer1301 formed over the buffer layer 1201. As discussed in greater detailbelow, the first conductive pillars (such as the first conductivepillars 1401 illustrated in FIGS. 14A and 14B) and the second conductivepillars (such as the second conductive pillars 1403 illustrated in FIGS.14A and 14B) will be formed in the openings 1305 and 1307, respectively,to provide electrical connections to the contact pads 1103. Furthermore,the conductive lines (such as the conductive lines 1405 illustrated inFIGS. 14A and 14B) will be formed in the openings 1309 to electricallyinterconnect pairs of the second contact pillars. In the illustratedembodiment, top-view shapes of the openings 1305 and 1307 are circles.However, in other embodiments, the top-view shapes of the openings 1305and 1307 may be polygons such as triangles, rectangles, hexagons, or thelike. In some embodiments, the openings 1305 and 1307 have a width W₄between about 33 μm and about 106 μm, such as about 50 μm, and theopenings 1309 have a width W₅ between about 15 μm and about 60 μm, suchas about 15 μm.

Referring to FIGS. 14A and 14B, the first conductive pillars 1401 areformed in combined openings formed by the openings 1305 and 1107, thesecond conductive pillars 1403 are formed in combined openings formed bythe openings 1307 and 1203, and the conductive lines 1405 are formed inthe openings 1309 (see FIGS. 13A and 13B). In some embodiments, thefirst conductive pillars 1401, the second conductive pillars 1403 andthe conductive lines 1405 may be formed using similar materials andmethods as the first conductive pillars 401, the second conductivepillars 403 and the conductive lines 405 (see, for example, FIGS. 4A and4B) and the description is not repeated herein. Accordingly, the firstconductive pillars 1401 and the second conductive pillars 1403 have thewidth W₄ of the openings 1305 and 1307, and the conductive lines 1405have the width W₅ of the openings 1309. In some embodiments, theconductive line 1405 is separated from two neighboring conductivepillars, such as the first conductive pillar 1401 and the secondconductive pillar 1403, by the first distance D₁ and the second distanceD₂, respectively, as illustrated in FIGS. 14A and 14B. In theillustrated embodiment, the second distance D₂ is larger than the firstdistance D₁. In other embodiments, the second distance D₂ may be lessthan or equal to the first distance D₁. In some embodiments, the firstdistance D₁ is between about 15 μm and about 50 μm, and the seconddistance D₂ is between about 15 μm and about 50 μm.

Referring further to FIGS. 14A and 14B, after forming the firstconductive pillars 1401, the second conductive pillars 1403 and theconductive lines 1405, the patterned mask 1303 is removed. In someembodiments, the patterned mask 1303 comprising a photoresist materialis removed using, for example, an ashing process followed by a wet cleanprocess. Subsequently, exposed portions of the seed layer 1301 areremoved using similar methods as the seed layer 301 (see, for example,FIGS. 4A and 4B) and the description is not repeated herein.

FIG. 14A illustrates that a top-view pattern of the routing layer,comprising the first conductive pillars 1401, the second conductivepillars 1403 and the conductive lines 1405. In some embodiments, atop-view pattern of the second conductive pillars 1403 and theconductive lines 1405 is similar to a top-view pattern of the bufferlayer 1201, with elements of the top-view pattern of the buffer layer1201 having larger sizes than similar elements of the top-view patternof the second conductive pillars 1403 and the conductive lines 1405. Insome embodiments, the buffer layer 1201 and the patterned mask 1303 maybe patterned using masks having features of same sizes. However, due toprocess variations, a same feature of a mask after being transferred tothe buffer layer 1201 and the patterned mask 1303 may have differentsizes depending on material properties of the buffer layer 1201 and thepatterned mask 1303, and patterning methods used. In the illustratedembodiment, an outer diameter of the ring-shaped structures 1205 islarger than the width W₄ of the second conductive pillars 1403, and awidth of the rectangular structures 1207 is larger than the width W₅ ofthe conductive lines 1405. In some embodiments, sidewalls of the secondconductive pillars 1403 are separated from corresponding outer sidewallsof the ring-shaped structures 1205 by the third distance D₃, andsidewalls of the conductive lines 1405 are separated from correspondingsidewalls of the rectangular structures 1207 by the third distance D₃.In some embodiments, the third distance D₃ may vary depending onproperties of patterned materials and patterning methods used.Accordingly, the outer diameter of the ring-shaped structures 1205 isequal to W₄+2D₃, and the width of the rectangular structures 1207 isequal to W₅+2D₃.

Referring to FIGS. 15A and 15B, a protective layer 1501 is formed overthe first conductive pillars 1401, the second conductive pillars 1403and the conductive lines 1405. In some embodiments, the protective layer1501 may be formed using similar materials and methods as the protectivelayer 501 (see, for example, FIGS. 5A and 5B) and the description is notrepeated herein. During the following description, the passivation layer1105, the buffer layer 1201, the protective layer 1501, the seed layer1301, the first conductive pillars 1401 the second conductive pillars1403 and the conductive lines 1405 may be collectively referred to as arouting structure 1503. In some embodiments, the processed wafer 1101may be singulated into individual semiconductor dies (such as thesemiconductor die 1100) by sawing, a laser ablation method, or the like.Subsequently, each of the dies may be tested to identify known good dies(KGDs) for further processing.

As described above, the buffer layer 1201 is interposed between thepassivation layer 1105 and the second conductive pillars 1403 and theconductive lines 1405. The use of buffer layer 1201 may advantageouslyallow reducing or eliminating formation of cracks in the passivationlayer 1105 and layers below, which may be caused, for example, bymismatch of coefficients of thermal expansion (CTE) between thepassivation layer 1105 and the second conductive pillars 1403 and theconductive lines 1405.

Referring further to FIGS. 15A and 15B, in some embodiments, the contactpads 1103 that are contacting the second conductive pillars 1403 may beelectrically decoupled from the various active and passive devices ofthe semiconductor die 1100 and may be also referred to as floatingcontact pads. Accordingly, in such embodiments, the second conductivepillars 1403 and the conductive lines 1405 are not directly coupled tothe various active and passive devices of the semiconductor die 1100. Asdescribed below in greater detail, in some embodiments, one or moreredistribution layers (RDLs) may be formed over the routing structure1503 after dicing the processed wafer 1101 into individual semiconductordies (such as the semiconductor die 1100). In some embodiments, the RDLsmay electrically couple the second conductive pillars 1403, thecorresponding contact pads 1103 and the conductive lines 1405 to thevarious active and passive devices of the semiconductor die 1100, forexample, by interconnecting the contact pads 1103 that are coupled tothe various active and passive devices of the semiconductor die 1100 tothe second conductive pillars 1403. In other embodiments, the RDLs maynot couple the second conductive pillars 1403, the corresponding contactpads 1103 and the conductive lines 1405 to the various active andpassive devices of the semiconductor die 1100. In such embodiments, thesecond conductive pillars 1403 and the conductive lines 1405 may act asredistribution lines for one or more external devices coupled to thesemiconductor die 1100. For example, a signal from a first externaldevice may travel through the RDLs to a first pillar of a pair of thesecond conductive pillars 1403, then through a corresponding conductiveline 1405 to a second pillar of the pair of the second conductivepillars 1403, then again thorough RDLs to reach a second external deviceor another RDL of the first external device, bypassing in the processthe various active and passive devices of the semiconductor die 1100. Byforming the routing structure 1503 on the semiconductor die 1100 beforeforming one or more RDLs, it is possible to advantageously simplify astructure of the RDLs. In some embodiments, the number of one or moreRDLs may be reduced, which in turn may reduce parasitic contributionsfrom eliminated layers of the one or more RDLs.

FIG. 16 is a flow diagram illustrating a method 1600 of forming asemiconductor die in accordance with some embodiments. The method 1600starts at step 1601, wherein a passivation layer (such as thepassivation layers 105, 605 or 1105) is formed over contact pads (suchas the contact pads 103, 603 or 1103) of a processed wafer (such as theprocessed wafers 101, 601 or 1101) as described above with reference toFIGS. 1A and 1B, 6A and 6B, or 11A and 11B. In some embodiments, thepassivation layer has first openings (such as the openings 107, 607 or1107) formed therein as described above with reference to FIGS. 1A and1B, 6A and 6B, or 11A and 11B. In step 1603, a buffer layer (such as thebuffer layers 201, 701 or 1201) is formed on the passivation layer andthe contact pads as described above with reference to FIGS. 2A and 2B,7A and 7B, or 12A and 12B. In some embodiments, the buffer layer hassecond openings (such as the openings 203, 703 or 1203) formed thereinas described above with reference to FIGS. 2A and 2B, 7A and 7B, or 12Aand 12B. In step 1605, a routing layer is formed in the second openingsand over the buffer layer as described above with reference to FIG.3A-4B, 8A-9B, or 13A-14B. In some embodiments, the routing layercomprises first conductive pillars (such as the first conductive pillars401, 901 or 1401), second conductive pillars (such as the secondconductive pillars 403, 903 or 1403) and conductive lines (such as theconductive lines 405, 905 or 1405) that interconnect pairs of the secondconductive pillars as described above with reference to FIGS. 4A and 4B,9A and 9B, or 14A and 14B. The first conductive pillars and the secondconductive pillars contact the conductive pads as described above withreference to FIGS. 4A and 4B, 9A and 9B, or 14A and 14B. In step 1607, aresulting structure is singulated to form individual dies (such as thesemiconductor dies 100, 600 or 1100) as described above with referenceto FIGS. 5A and 5B, 10A and 10B, or 15A and 15B.

FIGS. 17-21 are cross-sectional views of various processing steps duringfabrication of a stacked semiconductor device in accordance with someembodiments. As described below in greater detail, semiconductor dies(such as the semiconductor dies 100, 600 or 1100) will undergo variousprocessing steps to form the stacked semiconductor device 2100 (see, forexample, FIG. 21).

Referring first to FIG. 17, in some embodiments, a release layer 1703 isformed over a carrier 1701, and one or more dielectric layers 1705 isformed over the release layer 1703 to start forming a packagedsemiconductor device 1700. In some embodiments, the carrier 1701 may beformed of quartz, glass, or the like, and provides mechanical supportfor subsequent operations. In some embodiments, the release layer 1703may comprise a light to heat conversion (LTHC) material, a UV adhesive,or the like, and may be formed using a spin-on coating process, aprinting process, a lamination process, or the like. In someembodiments, the release layer 1703 formed of a LTHC material whenexposed to light partially or fully loses its adhesive strength and thecarrier 1701 can be easily removed from the back side of the packagedsemiconductor device 1700. In some embodiments, the one or moredielectric layers 1705 may be formed using similar materials and methodsas the passivation layer 105 (see, for example, FIGS. 1A and 1B) and thedescription is not repeated herein. In other embodiments, the one ormore dielectric layers 1705 may be formed using similar materials andmethods as the buffer layer 201 (see, for example, FIGS. 2A and 2B) andthe description is not repeated herein.

Referring further to FIG. 17, conductive vias 1707 are formed on the oneor more dielectric layers 1705. In some embodiments, a seed layer (notshown) is formed on the one or more dielectric layers 1705. The seedlayer seed may comprise copper, titanium, nickel, gold, the like, or acombination thereof, and may be formed using an electro-chemical platingprocess, ALD, PVD, sputtering, the like, or a combination thereof. Insome embodiments, a sacrificial layer (not shown) is formed over theseed layer. A plurality of openings is formed in the sacrificial layerto expose the seed layer. In some embodiments wherein the sacrificiallayer comprises a photoresist material, the sacrificial layer may bepatterned using suitable photolithography methods. In some embodiments,the openings are filled with conductive materials as such copper,aluminum, nickel, gold, silver, palladium, the like, or a combinationthereof using an electro-chemical plating process, ALD, the like, or acombination thereof to form the conductive vias 1707. After theformation of the conductive vias 1707, the sacrificial layer is thenremoved. In some embodiments wherein the sacrificial layer comprises aphotoresist material, the sacrificial layer may be removed using anashing process followed by a wet clean process. Subsequently, exposedportions of the seed layer are removed using, for example, a suitableetching process.

Referring to FIG. 18, semiconductor dies 1803 are attached to the one ormore dielectric layers 1705 using adhesive layers 1801. In someembodiments, the semiconductor dies 1803 are placed on the one or moredielectric layers 1705 using, for example, a pick and place apparatus.In other embodiments, the semiconductor dies 1803 may be placed on theone or more dielectric layers 1705 manually, or using any other suitablemethod. In some embodiments, the semiconductor dies 1803 may be formedusing similar method as the semiconductor dies 100, 600 or 1100 (see,for example, FIG. 1A-5B, 6A-10B, or 11A-15B) and the description is notrepeated herein. In some embodiments, the adhesive layer 1801 maycomprise an LTHC material, a UV adhesive, a die attach film, or thelike, and may be formed using a spin-on coating process, a printingprocess, a lamination process, or the like.

Referring further to FIG. 18, the semiconductor dies 1803 compriserouting structures 1805 formed on device sides (front sides) of thesemiconductor dies 1803. In some embodiments, the routing structures1805 may be formed using similar methods as the routing structures 503,1003 or 1503 (see, for example, FIG. 1A-5B, 6A-10B, or 11A-15B) and thedescription is not repeated herein.

Referring to FIG. 19, an encapsulant 1901 is formed over the carrier1701, and over and surrounding the semiconductor dies 1803 and theconductive vias 1707. In some embodiments, the encapsulant 1901 maycomprise a molding compound such as an epoxy, a resin, a moldablepolymer, or the like. The molding compound may be applied whilesubstantially liquid, and then may be cured through a chemical reaction,such as in an epoxy or resin. In other embodiments, the molding compoundmay be an ultraviolet (UV) or thermally cured polymer applied as a gelor malleable solid capable of being disposed around and between thesemiconductor dies 1803 and the conductive vias 1707.

Referring further to FIG. 19, in some embodiments, a resulting structureis planarized using a CMP, a grinding process, or the like. In someembodiment, the planarization process is performed until conductivepillars and conductive lines (not shown) of the routing structures 1805are exposed. In some embodiments, the top surfaces of the conductivepillars and the conductive lines are substantially coplanar with topsurfaces of the conductive vias 1707 and the encapsulant 1901.

Referring to FIG. 20, one or more redistribution layers (RDLs) 2001 areformed over the semiconductor dies 1803, the conductive vias 1707 andthe encapsulant 1901. In some embodiments, the RDLs 2001 comprise one ormore dielectric layers 2003 and one or more conductive features 2005disposed within the one or more dielectric layers 2003. In theillustrated embodiment, the one or more dielectric layers 2003 areformed using similar materials and methods as the buffer layer 201 (see,for example, FIGS. 2A and 2B) and the description is not repeatedherein. In some embodiments, each of the one or more dielectric layers2003 may be patterned to expose underlying conductive features. Forexample, a bottommost dielectric layer of the one or more dielectriclayers 2003 is patterned to expose the conductive vias 1707 and theconductive features of the routing structures 1805. In some embodiment,the one or more dielectric layers 2003 comprising photo-patternablematerials may be patterned using an acceptable photolithographytechnique. For example, the bottommost dielectric layer of the one ormore dielectric layers 2003 is exposed to light and subsequentlydeveloped and/or cured.

Referring further to FIG. 20, a first conductive feature (notindividually shown) of the one or more conductive features 2005 isformed over the bottommost dielectric layer of the one or moredielectric layers 2003. The first conductive feature may comprisevarious lines/traces (running “horizontally” across a top surface of thebottommost dielectric layer) and/or vias (extending “vertically” throughthe bottommost dielectric layer, and contacting the conductive vias 1707and the conductive features of the routing structures 1805). In someembodiments, a seed layer (not shown) is deposited over the bottommostdielectric layer. The seed layer may comprise copper, titanium, nickel,gold, manganese, the like, or a combination thereof, and may be formedby ALD, PVD, sputtering, the like, or a combination thereof.Subsequently, a photoresist material (not shown) is deposited over theseed layer and patterned to define the desired pattern for the firstconductive feature. A conductive material, such as copper, tungsten,aluminum, silver, gold, the like, or a combination thereof, is formed onthe seed layer by an electro-chemical plating process, an electrolessplating process, ALD, PVD, the like, or a combination thereof.Subsequently, the photoresist material is removed using appropriatephotoresist stripping process, such as an ashing processes followed by awet clean process. Exposed portions of the seed layer over thebottommost dielectric layer are removed using, for example, a suitableetching process. Subsequently, the process described above is applied toother dielectric layers of the one or more dielectric layers 2003 untilformation of the RDLs 2001 is completed.

FIG. 20 further illustrates a blow up of an interface between therouting structure 1805, comprising a protective layer 2013, a firstconductive pillar 2015, a second conductive pillar 2017 and a conductiveline 2019, and the RDLs 2001. In some embodiments, the protective layer2013, the first conductive pillar 2015, the second conductive pillar2017 and the conductive line 2019 may be formed using similar materialsand methods as the protective layer 501, the first conductive pillar401, the second conductive pillar 403 and the conductive line 405 (see,for example, FIGS. 5A and 5B), respectively, and the description is notrepeated herein. In the illustrated embodiment, the one or moreconductive features of the RDLs are in contact with the first conductivepillar 2015 and the second conductive pillar 2017.

Referring further to FIG. 20, underbump metallizations (UBMs) 2007 areformed over and electrically coupled to the RDLs 2001. In someembodiments, a set of openings (not shown) may be formed through thetopmost dielectric layer of the one or more dielectric layers 2003 toexpose the one more conductive features 2005 of the RDLs 2001. The UBMs2007 may extend through these openings in the topmost dielectric layerof the one or more dielectric layers 2003 and may also extend along asurface of the topmost dielectric layer of the one or more dielectriclayers 2003. The UBMs 2007 may include three layers of conductivematerials, such as a layer of titanium, a layer of copper, and a layerof nickel. However, one of ordinary skill in the art will recognize thatthere are many suitable arrangements of materials and layers, such as anarrangement of chrome/chrome-copper alloy/copper/gold, an arrangement oftitanium/titanium tungsten/copper, or an arrangement ofcopper/nickel/gold, that are suitable for the formation of the UBMs2007. Any suitable materials or layers of material that may be used forthe UBMs 2007 are fully intended to be included within the scope of thecurrent application. FIG. 20 further illustrates the formation ofconnectors 2009 over and electrically coupled to the UBMs 2007. In someembodiments, the connectors 2009 may be solder balls, metal pillars,controlled collapse chip connection (C4) bumps, ball grid array (BGA)balls, micro bumps, electroless nickel-electroless palladium-immersiongold technique (ENEPIG) formed bumps, or the like. The connectors 2009may include a conductive material such as solder, copper, aluminum,gold, nickel, silver, palladium, tin, the like, or a combinationthereof. In some embodiments in which the connectors 2009 are solderbumps, the connectors 2009 are formed by initially forming a layer ofsolder through commonly used methods such as evaporation,electroplating, printing, solder transfer, ball placement, or the like.Once the layer of solder has been formed on the structure, a reflow maybe performed in order to shape the material into the desired bumpshapes. In other embodiments, the connectors 2009 may be metal pillars(such as a copper pillar) formed by a sputtering, printing,electro-chemical plating, electroless plating, CVD, or the like. Themetal pillars may be solder free and have substantially verticalsidewalls. In some embodiments, a metal cap layer (not shown) is formedon the top of the metal pillars. The metal cap layer may include nickel,tin, tin-lead, gold, silver, palladium, indium, nickel-palladium-gold,nickel-gold, the like, or a combination thereof and may be formed by aplating process.

Referring further to FIG. 20, after forming the connectors 2009, thepackaged semiconductor device 1700 is detached from the carrier 1701 anddiced to form individual packages 2011. In some embodiments, thepackaged semiconductor device 1700 may be diced by sawing, a laserablation method, or the like. Subsequently, each of the packages 2011may be tested to identify known good packages (KGPs) for furtherprocessing.

FIG. 21 illustrates a bonding process of a workpiece 2105 to the package2011 with a set of connectors 2107 extending through openings in the oneor more dielectric layers 1705 to form a stacked semiconductor device2100. In some embodiments, the workpiece 2105 may be a package, one ormore dies, a printed circuit board, an interposer, or the like. In someembodiments wherein the workpiece 2105 is a package, the stackedsemiconductor device 2100 is a PoP device. In other embodiments whereinthe workpiece 2105 is a die, the stacked semiconductor device 2100 is aCoP device. In some embodiments, the connectors 2107 may be formed usingsimilar material and methods as the connectors 2009 (see, for example,FIG. 20) and the description is not repeated herein. In someembodiments, the workpiece 2105 may be bonded to the packagedsemiconductor device 1700 prior to dicing the packaged semiconductordevice 1700 into the packages 2011.

Referring further to FIG. 21, an underfill material (not shown) may beinjected or otherwise formed in the space between the workpiece 2105 andthe package 2011 and surrounding the connectors 2107. The underfillmaterial may, for example, be a liquid epoxy, deformable gel, siliconrubber, or the like, that is dispensed between the structures, and thencured to harden. This underfill material is used, among other things, toreduce damage to and to protect the connectors 2107.

Referring further to FIG. 21, in some embodiments, the stackedsemiconductor device 2100 may be bonded to a workpiece 2101 using theconnectors 2009. In some embodiments, the workpiece 2101 may be similarto the workpiece 2105 and the description is not repeated herein. In theillustrated embodiment, the workpiece 2101 is a printed circuit board(PCB).

As described above in greater detail, a package (such as the package2011) comprises a semiconductor die (such as the semiconductor die 1803)having a routing structure (such as the routing structure 1805) formedthereon. By forming the routing structure on the semiconductor diebefore forming one or more RDLs (such as the RDLs 2001), it is possibleto advantageously simplify a structure of the RDLs. In some embodiments,the number of the RDLs may be reduced, which in turn may reduceparasitic contributions from eliminated layers of the RDLs.

FIG. 22 is a flow diagram illustrating a method 2200 of forming astacked semiconductor device in accordance with some embodiments. Themethod 2200 starts with step 2201, wherein one or more dielectric layers(such as the one or more dielectric layers 1705) are formed over acarrier (such as the carrier 1701) as described above with reference toFIG. 17. Subsequently, conductive vias (such as the conductive vias1707) are formed over the one or more dielectric layers as describedabove with reference to FIG. 17. In step 2203, semiconductor dies (suchas the semiconductor dies 1803 formed using the method 1600) areattached to the one or more dielectric layers as described above withreference to FIG. 18. In some embodiments, the semiconductor diescomprise routing structures (such as the routing structures 1805 formedusing the method 1600). In step 2205, an encapsulant (such as theencapsulant 1901) is formed to encapsulate the conductive vias and thesemiconductor dies as described above with reference to FIG. 19. In step2207, one or more redistribution layers (such as the RDLs 2001) areformed over the encapsulated semiconductor dies and the conductive viasas described above with reference to FIG. 20. Subsequently, firstconnectors (such as the connectors 2009) are formed over the one or moreRDLs as described above with reference to FIG. 20. In Step 2209, theresulting structure is debonded from the carrier and diced to form apackage (such as the package 2011) as described above with reference toFIG. 20. In step 2211, a workpiece (such as the workpiece 2105) isbonded to the package using second connectors (such as the connectors2107), wherein the second connectors extent through the one or moredielectric layers and contact the conductive vias as described abovewith reference to FIG. 21.

According to an embodiment, a semiconductor device includes a die. Thedie includes contact pads thereon, and a routing structure over thecontact pads. The routing structure includes a passivation layer overthe contact pads, a buffer layer over the contact pads and thepassivation layer, first conductive pillars over a first set of thecontact pads, the first conductive pillars having first portions andsecond portions, the first portions extending through the passivationlayer and the buffer layer, the first portions contacting the first setof the contact pads, the second portions extending over the bufferlayer, and conductive lines over the buffer layer, the conductive linesconnecting pairs of the first conductive pillars. The semiconductordevice further includes an external connector structure over the routingstructure, the routing structure electrically coupling the contact padsto the external connector structure.

According to another embodiment, a semiconductor device includes a dieencapsulated by a molding structure. The die includes contact padsthereon, and a routing structure over the contact pads, the moldingstructure extending along sidewalls of the routing structure. Therouting structure includes a passivation layer over the contact pads,the passivation layer having first openings exposing a first set of thecontact pads and a second set of the contact pads, the first set of thecontact pads being different from the second set of the contact pads,and a buffer layer over the contact pads and the passivation layer, thebuffer layer having second openings exposing the second set of thecontact pads. The routing structure further includes first conductivepillars contacting the first set of the contact pads, the firstconductive pillars having first portions and second portions, the firstportions being disposed in the first openings and the second portionsextending above a topmost surface of the passivation layer, wherein eachof the first conductive pillars is spaced apart from other conductiveelements of the routing structure, second conductive pillars contactingthe second set of the contact pads, the second conductive pillars havingthird portions and fourth portions, the third portions being disposed inthe second openings, and the fourth portions extending above a topmostsurface of the buffer layer, and conductive lines over the buffer layer,ends of the conductive lines terminating with the second conductivepillars. The semiconductor device further includes an external connectorstructure over the routing structure, the routing structure electricallycoupling the contact pads to the external connector structure.

According to yet another embodiment, a method includes forming contactpads on a die. A passivation layer is blanket deposited over the contactpads. The passivation layer is patterned to form first openings, thefirst openings exposing the contact pads. A buffer layer is blanketdeposited over the passivation layer and the contact pads. The bufferlayer is patterned to form second openings, the second opening exposinga first set of the contact pads. First conductive pillars are formed inthe second openings, topmost surfaces of the first conductive pillarsbeing above a topmost surface of the buffer layer. Simultaneously withforming the first conductive pillars, conductive lines are formed overthe buffer layer, ends of the conductive lines terminating with thefirst conductive pillars. An external connector structure is formed overthe first conductive pillars and the conductive lines, the firstconductive pillars electrically coupling the contact pads to theexternal connector structure.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method comprising: forming contact pads on adie; depositing a passivation layer over the contact pads; patterningthe passivation layer to form first openings, the first openingsexposing a continuous portion of the contact pads across a firstdiameter of the first openings; depositing a buffer layer over thepassivation layer and the contact pads; patterning the buffer layer toform second openings and a third opening, the second openings exposing afirst set of the contact pads, the second openings having a seconddiameter less than the first diameter, the third opening being directlyover a portion of the passivation layer between two of the contact pads;forming first conductive pillars in the second openings, topmostsurfaces of the first conductive pillars being above a topmost surfaceof the buffer layer; simultaneously with forming the first conductivepillars, forming conductive lines over the buffer layer, ends of atleast one of the conductive lines terminating with the first conductivepillars; and forming an external connector structure over the firstconductive pillars and the conductive lines, the first conductivepillars electrically coupling the contact pads to the external connectorstructure.
 2. The method of claim 1, wherein forming the externalconnector structure comprises: encapsulating the die using anencapsulant, the encapsulant extending along sidewalls of the die, atopmost surface of the encapsulant being substantially coplanar with thetopmost surfaces of the first conductive pillars; forming one or moreredistribution layers over the first conductive pillars and theconductive lines, at least a portion of the one or more redistributionlayers extending over the encapsulant; and forming conductive bumps overthe one or more redistribution layers.
 3. The method of claim 1, whereintopmost surfaces of the conductive lines are substantially coplanar tothe topmost surfaces of the first conductive pillars.
 4. The method ofclaim 1, further comprising forming second conductive pillars in thefirst openings, topmost surfaces of the second conductive pillars beingsubstantially coplanar with the topmost surfaces of the first conductivepillars, wherein each of the second conductive pillars is electricallydecoupled from the first conductive pillars before forming the externalconnector structure.
 5. The method of claim 1, further comprisingbonding a package to the die, the external connector structure beinginterposed between the die and the package.
 6. The method of claim 1,further comprising forming a protective layer over the buffer layer, theprotective layer extending along sidewalls of the first conductivepillars and the conductive lines.
 7. The method of claim 1, wherein thesecond openings are within the first openings.
 8. A method comprising:forming contact pads over a die; forming a routing structure comprising:forming a passivation layer over the contact pads; forming a bufferlayer over the contact pads and the passivation layer; forming firstconductive pillars over a first set of the contact pads, the firstconductive pillars having first portions and second portions, the firstportions extending through the passivation layer and the buffer layer,the first portions contacting the first set of the contact pads, thesecond portions extending over the buffer layer, at least one of thesecond portions having a first bottom surface; forming conductive linesover the buffer layer, the conductive lines being formed simultaneouslywith the first conductive pillars, the conductive lines connecting pairsof the first conductive pillars, at least one of the conductive lineshaving a second bottom surface, the second bottom surface being ashorter distance from the die than the first bottom surface; and formingan external connector structure over the routing structure, the routingstructure electrically coupling the contact pads to the externalconnector structure.
 9. The method of claim 8, further comprisingbonding a package to the die, the external connector structure beinginterposed between the die and the package.
 10. The method of claim 8,further comprising: forming an encapsulant extending along sidewalls ofthe die, a topmost surface of the encapsulant being substantiallycoplanar with a topmost surface of the routing structure, whereinforming the external connector structure comprises: forming one or moreredistribution layers on the routing structure, at least a portion ofthe one or more redistribution layers extending along the topmostsurface of the encapsulant; and forming conductive bumps on the one ormore redistribution layers.
 11. The method of claim 8, wherein a widthof the first conductive pillars is larger than a width of the conductivelines.
 12. The method of claim 8, wherein a width of the second portionsof the first conductive pillars is larger than a width of the firstportions of the first conductive pillars.
 13. The method of claim 8,wherein forming the routing structure further comprises: forming secondconductive pillars over a second set of the contact pads, the secondconductive pillars having third portions and fourth portions, the thirdportions extending through the passivation layer and contacting thesecond set of the contact pads, the fourth portions extending over thepassivation layer, each of the second conductive pillars beingdisconnected from other conductive elements of the routing structure.14. The method of claim 13, wherein forming the routing structurefurther comprises: forming a protective layer, the protective layerextending along sidewalls of the first conductive pillars, the secondconductive pillars, and the conductive lines.
 15. A method comprising:forming contact pads over a die; forming a passivation layer over thecontact pads; patterning the passivation layer to have one or more firstopenings exposing a first set of contact pads; conformally depositing abuffer layer over the contact pads and the passivation layer; patterningthe buffer layer to have one or more second openings exposing a secondset of contact pads; forming a first set of conductive pillars over thefirst set of contact pads and the passivation layer, the first set ofconductive pillars contacting the first set of contact pads; forming asecond set of conductive pillars over the second set of contact pads andthe buffer layer, the second set of conductive pillars contacting thesecond set of contact pads; forming conductive lines over the bufferlayer, one of the conductive lines connecting a pair of the second setof conductive pillars; forming a protective layer over the first set ofconductive pillars and the second set of conductive pillars; and formingan external connector structure over the first set of conductivepillars, the second set of conductive pillars, the passivation layer,and the buffer layer.
 16. The method of claim 15, wherein forming theexternal connector structure comprises: forming one or moreredistribution layers, at least a portion of the one or moreredistribution layers extending along a topmost surface of theprotective layer; and forming conductive bumps on the one or moreredistribution layers.
 17. The method of claim 15, further comprisingbonding a package to the die, the external connector structure beinginterposed between the die and the package.
 18. The method of claim 15,wherein a width of the first openings is greater than a width of thesecond openings.
 19. The method of claim 15, wherein a topmost surfaceof the protective layer is substantially coplanar with topmost surfacesof the first set of conductive pillars and topmost surfaces of thesecond set of conductive pillars.
 20. The method of claim 15, whereintopmost surfaces of second set of conductive pillars are substantiallycoplanar with topmost surfaces of the conductive lines.